DULLES, Va.Aug. 31, 2004--

             Company Completes Second Successful Flight of
                     Ramjet-Powered Target Vehicle

Orbital Sciences Corporation (NYSE:ORB) announced today that it carried out another successful flight test of the GQM-163A Supersonic Sea-Skimming Target (SSST) system for the United States Naval Air Systems Command (NAVAIR) on August 27, 2004. The flight test, conducted at the Navy's missile test range in southern California, is part of a series of flights Orbital will conduct under the company's SSST Engineering and Manufacturing Development (EMD) contract from NAVAIR. Orbital was awarded the EMD contract in 2000 to meet the Navy's requirement for an affordable SSST to simulate supersonic anti-ship cruise missiles for fleet training and weapon systems research, development, test and evaluation. Orbital is scheduled to conduct several more flight tests of the Coyote target vehicle through the end of the year.

"We are very pleased with the results of the recent flight test of the Coyote target vehicle," said Mr. Keven Leith, Vice President of Navy Programs for Orbital's Launch Systems Group. "By meeting all the objectives for the flight test, we believe we are well down the road toward moving the program from its developmental phase to providing the Navy with a robust operational anti-ship target system."

The GQM-163A "Coyote" target missile design integrates a four-inlet, solid-fuel ducted rocket ramjet propulsion system into a compact missile airframe 18 feet long and 14 inches in diameter. Ramjet supersonic takeover speed is achieved using a decommissioned Navy MK 70 solid rocket motor for the first stage. Rail-launched from Navy test and training ranges, the highly maneuverable GQM-163A Coyote achieves cruise speeds of Mach 2.5+ following the separation of the MK 70 first-stage booster. The range of the target vehicle system is approximately 50 nautical miles at altitudes of less than 20 feet above the sea surface.

This most recent flight test of the GQM-163A Coyote vehicle was the second consecutive success for the program, following a successful flight carried out earlier this year in May. The primary objectives for this test, all of which were achieved, included the verification of booster ignition and stable first stage flight, the verification of the transition of the ducted rocket ramjet from booster separation to inlet start, and verification of the ducted rocket ramjet ignition, navigation to waypoint capability, verification of the laser altimeter performance, and initial horizontal weave and vertical maneuver performance verification. In addition, the test target missile was heavily instrumented in order to collect flight environment data to refine aerodynamic and guidance models for future missions.

Orbital is currently the only U.S. Department of Defense prime contractor to be both developing and operating ramjet-powered missile systems. In addition to developing the GQM-163A Coyote, Orbital provides the Navy with launch services for the MQM-8 VANDAL SSST. The MQM-8 VANDAL is based on the liquid-fuel ramjet-powered Talos missile and provides the Navy with a legacy SSST until the more capable GQM-163A Coyote is operational.

Orbital is developing and manufacturing the GQM-163A Coyote at its launch vehicle engineering and production facility in Chandler, Arizona. Orbital's major subcontractors include Aerojet Corporation in Gainesville, Virginia and Sacramento, California for the solid-fuel ducted rocket motor and CEi in Sacramento, California for the vehicle's avionics system.

Orbital develops and manufactures small space and rocket systems for commercial, military and civil government customers. The company's primary products are satellites and launch vehicles, including low-orbit, geosynchronous and planetary spacecraft for communications, remote sensing, scientific and defense missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense systems that are used as interceptor and target vehicles. Orbital also offers space-related technical services to government agencies and develops and builds satellite-based transportation management systems for public transit agencies and private vehicle fleet operators.

More information about Orbital can be found at http://www.orbital.com


Notes to Editors:

--  A Fact Sheet on the GQM-163A Coyote SSST can be found on Orbital's
    web site at:
    http://www.orbital.com/NewsInfo/Publications/index.html

--  High-resolution photos and artist renderings of the GQM-163A
    Coyote SSST, suitable for publication, are available on Orbital's
    web site at:
    http://www.orbital.com/NewsInfo/Images/MissileDefense/index.html


    CONTACT: Orbital Sciences Corporation
             Barron Beneski, 703-406-5528
             beneski.barron@orbital.com

    SOURCE: Orbital Sciences Corporation